The United States has abandoned its embassy in Chad, evacuating all but four diplomats who are now stationed at the N'Djamena airport amid heavy fighting between government forces and rebels in the capital.

The downtown embassy, which was hit by indirect fire during weekend clashes, is now vacant and unprotected and the State Department on Monday warned the rebels not to enter the compound, which remains sovereign U.S. territory.

"We would tell anybody who has any thoughts of entering the embassy grounds that that is American territory, leave it immediately and do not attempt to enter any of the buildings," spokesman Sean McCormack said. He said the warning is being sent to the rebels "through various channels" but acknowledged there was no guarantee the compound would not be breached.

At the same time, he said that suspected Sudanese support for the rebels was "very worrying" and that Washington had told the government of Sudan to end such backing and also press the rebels to withdraw. Those messages were conveyed directly to the Sudanese presidency and foreign ministry by the top U.S. diplomat in Khartoum, he said.

The rebels arrived on the capital's outskirts Friday after a three-day push across the desert from Chad's eastern border with Sudan and the situation in N'Djamena deteriorated over the weekend to the point where the State Department ordered several dozen nonessential U.S. embassy staff and their families to leave the country.

The four who remain _ Ambassador Louis Nigro, a defense attache, political counselor and security officer _ shredded and burned sensitive documents and removed the flag from the compound on Saturday before heading to the airport where they are now based, officials said.

McCormack said he the decision to abandon the embassy, a rare step believed to be the first such move since the U.S. mission to Liberia was fully evacuated during that country's civil war, was made because of "very fluid" security situation but stressed he expected the diplomats to return once conditions improve.

The State Department has urged U.S. citizens to leave Chad, and officials said a little under 100 of the roughly 500 registered with the embassy have gone.

Without any personnel at its embassy, the State Department has set up two telephone numbers to report the presence and whereabouts of Americans in Chad. Those numbers are (888) 407-4747 from the United States and Canada and (202) 501-4444 from overseas.

However, on Sunday, the department said its ability to help Americans in Chad was "extremely limited" and asked those who wished to be evacuated to "prepare to depart immediately and identify themselves to the French military, who will retrieve American citizens to escort them to the airport."

France, the former colonial power, has a long-standing military presence in Chad and is evacuating hundreds of foreigners from the country.

On Monday, the U.N. Security Council strongly condemned the rebel attacks and it gave a green light for France and other countries to help the government repel the threat.

In Chad, government forces were clashing with rebels for a third day with gunfire and shelling heard throughout the city. Thousands of people were fleeing and casualties were believed to be high.

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